Copper redistribution layer process for GaAs MMICs

A new copper metallization process is proposed that fabricates a redistribution layer on GaAs MMICs (monolithic microwave integrated circuits). This process enables the placement of Cu bonding pads and Cu pillar bumps over an MMIC. PBO (polybenzoxazole) is used as the low-k dielectric polymer for isolation. The thickness of the PBO layer is designed to be 10 mm in order to minimize the parasitic capacitance introduced by bonding pads placed on the active region of a HEMT (high electron mobility transistor). A single-pole double-throw HEMT switch fabricated by the proposed process exhibits good RF performance with negligible effect of the bonding pads.